import java.util.Scanner;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: ${USER}
 * Date: ${YEAR}-${MONTH}-${DAY}
 * Time: ${TIME}
 */
public class Main {
    public static int fibo(int x){
        int a = 0,b = 1,sum = 0;
        if(x == 1){
            return a;
        }
        if(x == 2){
            return b;
        }else{
            for (int i = 0; i < x; i++) {
                sum = a + b;
                a = b;
                b = sum;
            }
        }
        return sum;
    }
    public static void main(String[] args) {
        System.out.println("请输入要求项");
        Scanner scan = new Scanner(System.in);
        int input = scan.nextInt();
        System.out.println(fibo(input));
    }
}